:root{
  --bg:#f7f8fb; --surface:#fff; --text:#1d2433; --muted:#5b6475; --line:#e3e7ef;
  --brand:#1f5fbf; --brand-2:#0e9f8a; --accent:#e8a33d; --danger:#c8423b; --ok:#1f8a4c;
  --radius:14px; --shadow:0 2px 10px rgba(20,30,60,.06);
}
@media (prefers-color-scheme: dark){
  :root{ --bg:#11151d; --surface:#1a202b; --text:#e8ecf3; --muted:#9aa4b6; --line:#2a3240;
         --brand:#6ea4ff; --brand-2:#3cc9b2; --shadow:none; }
}
*{box-sizing:border-box}
html{-webkit-text-size-adjust:100%}
body{margin:0;background:var(--bg);color:var(--text);
  font-family:"Noto Sans Lao","Phetsarath OT","Noto Sans",system-ui,sans-serif;line-height:1.75;font-size:16px}
a{color:var(--brand);text-decoration:none} a:hover{text-decoration:underline}
img{max-width:100%;height:auto}
.container{max-width:1100px;margin:0 auto;padding:0 16px}
.narrow{max-width:780px}
header.site{background:var(--surface);border-bottom:1px solid var(--line);position:sticky;top:0;z-index:20}
header.site .bar{display:flex;align-items:center;gap:16px;min-height:60px;flex-wrap:wrap}
.logo{font-weight:700;font-size:1.15rem;color:var(--text)} .logo span{color:var(--brand)}
nav.main{display:flex;gap:14px;flex-wrap:wrap;margin-left:auto;align-items:center;font-size:.95rem}
nav.main a{color:var(--text)}
.btn{display:inline-block;border:0;border-radius:10px;padding:.55rem 1rem;font:inherit;cursor:pointer;
  background:var(--brand);color:#fff;font-weight:600}
.btn:hover{filter:brightness(1.08);text-decoration:none}
.btn.secondary{background:transparent;color:var(--brand);border:1.5px solid var(--brand)}
.btn.ghost{background:var(--line);color:var(--text)}
.btn.sm{padding:.3rem .7rem;font-size:.9rem}
.btn:disabled{opacity:.5;cursor:not-allowed}
main{padding:28px 0 60px}
.card{background:var(--surface);border:1px solid var(--line);border-radius:var(--radius);padding:20px;box-shadow:var(--shadow)}
.grid{display:grid;gap:16px;grid-template-columns:repeat(auto-fill,minmax(250px,1fr))}
.hero{padding:48px 0 24px}
.hero h1{font-size:clamp(1.7rem,4vw,2.6rem);line-height:1.4;margin:0 0 12px}
.hero p{color:var(--muted);font-size:1.1rem;max-width:640px}
.muted{color:var(--muted)} .small{font-size:.88rem}
.badge{display:inline-block;font-size:.75rem;padding:.1rem .55rem;border-radius:99px;background:var(--line);color:var(--muted)}
.badge.premium{background:#fff3dc;color:#9a6200} .badge.done{background:#dff5e8;color:var(--ok)}
.messages{list-style:none;padding:0;margin:0 0 16px}
.messages li{padding:.7rem 1rem;border-radius:10px;margin-bottom:8px;background:#e8f0ff;color:#1b3d75}
.messages li.success{background:#e2f6ea;color:#17603a} .messages li.error{background:#fde7e5;color:#8b2620}
.messages li.warning{background:#fff4dd;color:#7a5300}
.progress{height:10px;background:var(--line);border-radius:99px;overflow:hidden}
.progress>span{display:block;height:100%;background:linear-gradient(90deg,var(--brand),var(--brand-2))}
.lesson-list{list-style:none;padding:0;margin:8px 0 0}
.lesson-list li{display:flex;justify-content:space-between;gap:8px;padding:8px 0;border-top:1px dashed var(--line)}
article.lesson h2{margin-top:1.8em;border-left:4px solid var(--brand);padding-left:10px}
article.lesson table{border-collapse:collapse;width:100%;display:block;overflow-x:auto}
article.lesson th,article.lesson td{border:1px solid var(--line);padding:6px 10px;text-align:left}
pre{background:#0f1622;color:#e6edf3;padding:14px;border-radius:10px;overflow-x:auto;font-size:.9rem;line-height:1.5}
code{font-family:"JetBrains Mono",Consolas,monospace}
blockquote{margin:1em 0;padding:.6em 1em;background:var(--surface);border-left:4px solid var(--accent);border-radius:6px}
.two-col{display:grid;grid-template-columns:minmax(0,1fr) 340px;gap:24px}
@media (max-width:900px){.two-col{grid-template-columns:minmax(0,1fr)}}
.sticky{position:sticky;top:80px}
form p{margin:0 0 12px}
input[type=text],input[type=email],input[type=password],input[type=number],select,textarea{
  width:100%;padding:.6rem .75rem;border:1px solid var(--line);border-radius:10px;background:var(--surface);color:var(--text);font:inherit}
textarea{resize:vertical}
.helptext,.errorlist{font-size:.85rem;color:var(--muted)} .errorlist{color:var(--danger);padding-left:18px}
.quiz .q{margin-bottom:18px} .quiz label{display:block;padding:6px 10px;border:1px solid var(--line);border-radius:8px;margin:6px 0;cursor:pointer}
.quiz label:hover{border-color:var(--brand)}
.result.ok{border-left:4px solid var(--ok)} .result.bad{border-left:4px solid var(--danger)}
.chat-box{height:min(60vh,560px);overflow-y:auto;display:flex;flex-direction:column;gap:12px;padding:6px}
.msg{max-width:88%;padding:10px 14px;border-radius:14px;word-wrap:break-word;overflow-wrap:anywhere}
.msg.user{align-self:flex-end;background:var(--brand);color:#fff;border-bottom-right-radius:4px}
.msg.assistant{align-self:flex-start;background:var(--surface);border:1px solid var(--line);border-bottom-left-radius:4px}
.msg .meta{font-size:.72rem;opacity:.7;margin-bottom:2px}
.msg pre{white-space:pre-wrap}
.chat-input{display:flex;gap:8px;margin-top:12px} .chat-input textarea{flex:1}
.seg{display:inline-flex;border:1px solid var(--line);border-radius:10px;overflow:hidden}
.seg label{padding:.35rem .8rem;cursor:pointer;font-size:.9rem}
.seg input{display:none} .seg input:checked+span{color:var(--brand);font-weight:700}
.price{font-size:1.8rem;font-weight:700}
.plan.featured{border:2px solid var(--brand)}
.plan ul{padding-left:18px}
.lab-canvas{width:100%;background:var(--surface);border:1px solid var(--line);border-radius:12px;touch-action:none}
.toolbar{display:flex;flex-wrap:wrap;gap:8px;align-items:center;margin:12px 0}
.stat{display:inline-block;padding:4px 10px;background:var(--line);border-radius:8px;font-size:.9rem}
.gallery{display:grid;grid-template-columns:repeat(auto-fill,minmax(180px,1fr));gap:12px}
.gallery figure{margin:0} .gallery img{border-radius:10px;border:1px solid var(--line);aspect-ratio:1;object-fit:cover;width:100%}
.gallery figcaption{font-size:.8rem;color:var(--muted)}
footer.site{border-top:1px solid var(--line);background:var(--surface);padding:28px 0;font-size:.9rem;color:var(--muted)}
footer.site .cols{display:flex;flex-wrap:wrap;gap:28px;justify-content:space-between}
footer.site a{color:var(--muted)}
.puzzle{display:grid;grid-template-columns:repeat(3,64px);gap:6px}
.puzzle div{height:64px;display:flex;align-items:center;justify-content:center;font-size:1.6rem;font-weight:700;
  border-radius:10px;background:var(--brand);color:#fff} .puzzle div.blank{background:var(--line)}
.legal h2{font-size:1.2rem;margin-top:1.6em}
.cookie{position:fixed;left:16px;right:16px;bottom:16px;max-width:640px;margin:auto;z-index:50}
[hidden]{display:none!important}